The present invention relates to journal bearing devices for use in rotary assemblies, and more particularly to a bearing type bushing device that is suitable for forming multiple pre-aligned bearing surface regions in such a rotary assembly. Journal or rotary assemblies which include a shaft and a free spinning member for relative rotary motion, are well known. Examples of such rotary assemblies include idler gears, idler pulleys, idler rollers, and the like. The use of bearings or bushings, for example, plain journal bearings or bushings to support the idler on the shaft in such an assembly, and to reduce the friction of motion between the shaft and free spinning member, is also well known. Typically, the bearing or bushing device is fitted into a mounting or bushing hole formed in the free spinning member, and the shaft is then received through a central bore or opening in the bearing or bushing device.
The material, size and shape of the bearing or bushing device ordinarily are selected in order to reduce the friction of motion,and in order to maximize the efficiency of motion between the shaft and bearing or bushing device. Furthermore, in order to reduce the risk of vibration (i.e. wobbling) and of misalignment between the shaft and bearing or bushing, such bearing or bushing device should be made as long as the portion of the shaft journaled in or through the mounting hole of the free spinning member. Unfortunately however, there are problems and limitations regarding the effective length of such a journal bearing or bushing device.
This is in part because the longer the bearing or bushing, the greater the bearing surface area, and therefore possibly the greater the friction force to overcome. In addition, the load bearing capacity of a bearing or bushing in such a rotary assembly has been shown to depend in significant part on the length-to-diameter ratio of the bearing or bushing device. Ordinarily, this ratio is recommended to be within the range of 1 to 2, the result of which is usually a relatively short journal bearing or bushing device. Longer bearings or bushing devices with a length-to-diameter ratio of 3 to 4 are recommended, but only for light load assemblies, and only if the journal bearing or bushing device is self-aligning to the shaft.
These problems and limitations are particularly of concern with respect to the design of journal bearings or bushings for rotary assemblies which include wide free spinning members or idlers such as long idler rollers, wide idler pulleys,wide idler gears or the like which each have a deep hub and bushing hole therethrough. Such rotary assemblies therefore require a relatively longer bearing or bushing device. As those skilled in the art recognize, there has been a need for a simple, suitable and low cost journal bearing or bushing for use with such rotary assemblies.
As disclosed for example in Xerox Disclosure Journal, p.33 Vol. 13 No. 1, the conventional practice when a long bearing or bushing is needed for such a deep bushing hole, has been to use a pair of such bearings or bushings, fitting one from each end of the bushing or mounting hole of the free spinning member. The use of multiple bearings or bushings as such is relatively more expensive than the use of a single piece, long bearing or bushing. On the other hand, conventional self-aligning bearings or bushings are ordinarily short, or include multiple separate parts. Consequently, they are not individually suitable for wide free spinning members having a deep mounting or bushing hole, or they are relatively more expensive to manufacture and to assemble than is a single piece bearing or bushing.
For example, U.S. Pat. No. 3,942,403 issued Mar. 9, 1976, to Pramberger discloses a short and therefore unsuitable single unit bushing device for inserting into a bushing hole of mating piano action members. The disclosed bushing device is made of a suitable plastic or elastomeric material and includes one flanged end and a single raised midpoint that is compressed upon assembly of the bushing around a journaled pin. The compression causes an inner bore of the bushing to form a single, substantially line contact bearing surface with the journaled pin.
U.S. Pat. No. 4,196,503 issued Apr. 8, 1980, to McCloskey discloses a complicated and therefore relatively expensive spherical bearing assembly that is made up of multiple separate and compressible inner and outer parts. During assembly, the outer parts are compressed causing the inner part to form a single uniform self-aligning bearing surface against a journaled shaft.
U.S. Pat. No. 4,489,992 issued Dec. 25, 1984, to Brandenstein et al. discloses a short self-aligning bearing assembly of multiple, separate parts that includes an outer a sleeve which is covered with an elastic plastic jacket. The jacket has a single raised annular ridge on it that is press fitted upon assembly into a bushing hole, thereby compressing the plastic jacket and forcing the bushing sleeve into alignment against a journaled shaft.